Thermosetting resins, having a characteristic cross-linking structure to exhibit high heat resistance and dimensional stability, are widely used in fields requiring high reliability (e.g., electronic components). Particularly, a copper-clad laminated sheet or an interlayer dielectric material must have high adhesion-to-copper foil property for micro-wiring formation, or good processability for provision of, for example, holes through drilling or punching, so as to meet recent requirements for high-density technology. Also, in view of recent environmental problems, such a material must have heat resistance and flame retardancy superior to those of conventional ones, so as to meet requirements for mounting of electronic components by use of lead-free solder, or flame retardancy without use of a halogen-containing flame retardant. Meanwhile, from the viewpoints of the product safety and improvement of working environment, demand has arisen for a thermosetting resin composition which contains only less toxic components and does not generate, for example, toxic gas.
Bismaleimide compound, which is a thermosetting resin, exhibits good dielectric properties, flame retardancy, and heat resistance. However, since no known bismaleimide compound exhibits curing reactivity to epoxy resin, when such a compound is used as is in an epoxy-curing thermosetting resin, the resin exhibits insufficient heat resistance.
Therefore, there is disclosed a method in which an addition product of a bismaleimide compound and aminophenol is produced through kneading under heating, and the product is used as a curing agent in an epoxy-curing thermosetting resin composition (Patent Document 1 or 2). However, the method disclosed in Patent Document 1 or 2 produces an addition product of a bismaleimide compound and aminophenol at low yield. In addition, when a thermosetting resin composition containing the addition product is used in a copper-clad laminated sheet or an interlayer dielectric material, the sheet or material exhibits, for example, poor heat resistance and processability.
A variety of thermosetting resin compositions each containing melamine resin or a guanamine compound are already known (Patent Documents 3, 4, 5, 6, and 7).
Although melamine resin (thermosetting resin) or a guanamine compound exhibits good adhesion, flame retardancy, and heat resistance, the resin or the compound has poor solubility in an organic solvent and thus poses problems in that, for example, a thermosetting resin composition is difficult to prepare therefrom unless a highly toxic N-containing organic solvent (e.g., N,N-dimethylformamide) is used in a large amount, and, in addition, the thus-prepared composition exhibits poor storage stability.
Furthermore, a copper-clad laminated sheet or interlayer dielectric material formed from such a thermosetting resin composition poses a problem in terms of contamination of a chemical liquid (e.g., plating liquid) during production of, for example, an electronic component.
Thermosetting resin compositions each containing melamine resin or a thermosetting resin prepared through condensation of a guanamine compound by use of an aldehyde (e.g., formaldehyde) have improved solubility in an organic solvent. However, since those thermosetting resin compositions have low thermal decomposition temperature and generate toxic decomposition gas, the compositions may impair the working environment. In addition, such thermosetting resin compositions exhibits low heat resistance to recently required lead-free solder or insufficient copper cladding heat resistance. Since the thermosetting resin compositions exhibit insufficient adhesion-to-copper foil property, flexibility, or toughness for fine processing or wiring formation, the compositions may cause problems in that, for example, disconnection or exfoliation occurs in a circuit pattern, and cracking occurs during formation of, for example, holes through drilling or punching.
A methylolated guanamine resin is also disclosed (Patent Document 8). However, similar to the case of the aforementioned compositions, the resin poses problems in terms of, for example, heat resistance, adhesion, and processability.
Also, a thermosetting resin composition containing an addition product of a bismaleimide compound and aminobenzoic acid is disclosed (Patent Document 9). However, a cured product of the resin composition has low thermal decomposition temperature and exhibits low heat resistance to recently required lead-free solder or insufficient copper cladding heat resistance. The resin composition has poor solubility in an organic solvent and poses problems in terms of, for example, processability.    Patent Document 1: Japanese Patent Publication (kokoku) No. S63-034899    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. H06-032969    Patent Document 3: Japanese Patent Publication (kokoku) No. S62-046584    Patent Document 4: Japanese Patent Application Laid-Open (kokai) No. H10-067942    Patent Document 5: Japanese Patent Application Laid-Open (kokai) No. 2001-011672    Patent Document 6: Japanese Patent Application Laid-Open (kokai) No. H02-258820    Patent Document 7: Japanese Patent Application Laid-Open (kokai) No. H03-145476    Patent Document 8: Japanese Patent Publication (kokoku) No. S62-061051    Patent Document 9: Japanese Patent Publication (kokoku) No. H06-008342